Ion beams can be and are used in sputtering techniques, substrate cleaning, co-deposition of materials, ion assisted deposition and ion sputtering. The present device can be and is advantageously used in any and all of the above mentioned applications. However, the present device per se, and the utility of the present device will be described in connection with the fabrication of a thin film device through ion assisted deposition, by way of example.
It is well understood that, if ion beams are employed in an ion assisted deposition during the preparation of thin film devices, the resulting thin films are characterized by many desirable properties which are otherwise not present. For instance there is improved film packing density, improved stoichiometry and improved adhesion. The technique of using ion beams as part of a thin film deposition activity has also been used to modify stress in the deposited film and to reduce water vapor absorption as related to the film deposition. In particular with regard to optical thin film coatings, the refractive index is increased and the optical thin film stacks possess greater (long term) stability. It is believed that ion bombardment, of both the substrate and the material being deposited, removes atoms that are not firmly entrenched in the substrate while at the same time other atoms of the material are driven more completely into the substrate. In addition greater surface mobility for condensing atoms is provided. As should be apparent a film characterized by denser packing and better adhesion results, if an ion beam is employed during thin film deposition.
In a number of ion involved applications, an ion source capable of producing ions over a broad area, in response to applied low energy and low current, is required. In the prior art it has become the practice to employ a hot cathode along with a magnetic multipole source in order to obtain large area beams of ions having sufficient current density and beam energy. Hot cathode sources are very versatile and can be designed to produce beams of different sized areas and different current and energy intensities. However since the hot cathode devices employ hot filament cathodes to thermionically supply electrons, these arrangements have relatively short lifetimes, i.e. matters of hours. Typically for a 0.4 mm diameter tungsten wire, the filament lifetime is in the order of a few hours. If larger diameters are used, such as 1.5 mm, the lifetime may be 10 to 30 hours. However, thicker filaments require higher heating currents for instance in the range of 60 to 70 amperes. In addition hot filaments have been found to require large ionization discharge chambers as well as large power sources.
The present system, which is a cold cathode system, provides all of the desirable features of a hot filament, magnetic multipole source, while not requiring a large ionization discharge chamber and not being characterized by a short filament lifetime.